The instruments currently used for measuring Q-quality of oscillatory circuit components in ultra short wave and microwave ranges are, as a rule, manually operated, thus failing to provide for high accuracy of measurements, and are intended only for linear oscillatory circuit components.
With this in view, there has developed a demand for a high-precision automatic digital Q-meter that would measure with higher accuracy parameters of both linear and nonlinear radio components in low and moderate electromagnetic fields, and provide for high-speed operation.
Known in the art is an apparatus for measuring the Q-quality of oscillatory circuit components (cf. USSR Inventor's Certificate No. 519,650; C1. GO1R 27/26) which includes a control unit whose sawtooth generator is electrically coupled to a high-frequency generator connected to a frequency modulator, the output of which is connected to a measuring unit electrically coupled, in turn, to the oscillatory circuit components whose Q-quality is to be measured, and a unit for producing the first frequency derivative of the amplitude-frequency response of the oscillatory circuit, said unit being connected to the control unit null device connected in series with the control unit sawtooth generator, to a unit for producing the second frequency derivative of the amplitude-frequency response of the oscillatory circuit, and to a peak detector connected, in turn, to the measuring unit.
The apparatus also includes a step voltage generator connected to the units for producing the first and second frequency derivatives of the amplitude-frequency response of the oscillatory circuit and electrically coupled to the frequency modulator. Furthermore, the apparatus includes an amplifier, the drive input of which is connected to the step voltage generator and the output, to the drive input of the frequency modulator, while another input thereof is electrically coupled to the unit for producing the second frequency derivative of the amplitude-frequency response of the oscillatory circuit. Also included in the apparatus are an attenuator connected to the unit for producing the second frequency derivative of the amplitude-frequency response of the oscillatory circuit and electrically coupled to the amplifier input, a subtracting unit connected, in turn, to the amplifier, attenuator and to the units for producing the first and second frequency derivatives of the amplitude-frequency response of the oscillatory circuit, the output of the subtracting unit being electrically coupled to a Q-readout unit.
The apparatus fails to provide for high accuracy of measuring the Q-quality in a wide frequency range because of the frequency dependence of transfer ratios of the measuring unit coupling elements and due to errors associated with maintaining the measuring unit input voltage constant, since the second frequency derivative of the amplitude-frequency response, of the oscillatory circuit in said apparatus is used as an absolute analog value for measuring the Q-quality and depends on the transfer ratios of coupling elements and on the absolute value of the input voltage of the measuring unit.